1. Field of the Invention
The present invention relates to an apparatus for exposing an optical disc master plate, and in particular, to an exposing apparatus for exposing an optical disk master plate which exposes a photoresist master plate and writes in a DVD-R (Digital Video Disc Recordable) format therein, and a method of exposing an optical disc master plate.
2. Discussion of the Background Art
According to a document, entitled "DVD Specifications for Recordable Disc/part 1. Physical Specification Version 0.9 April 1997", the DVD-R disc format forms a wobble track recorded with a sinusoidal wave signal of constant frequency for use in the synchronization of disc rotation and a land pre-pit for storing address information, etc., over the entire information area. The land pre-pit is the pit disposed on the land between the wobble tracks, and is formed in constant relationship with the wobble phase of the track. FIG. 13 is a graph showing the phase relationship between the wobble signal and the pre-pit signal.
As shown in FIG. 14, the land pre-pit employs a 2-sync.-frame length as one unit and sets an even number position and an odd number position at the head portion each of two 1-sync.-frame lengths. The length of 1-sync.-frame equals the length of an 8-wobble period. An overlap between the tracks on which the land pre-pits are formed adjacently to each other can be avoided by changing the position thereof, so that the land pre-pit is successively formed on a spiral track. If the land pre-pits overlap each other, the land pre-pit signal cannot be correctly reproduced at the time of DVD-R (format) reproduction. However, in regard to the exposing apparatus of the optical disc master plate for exposing the photoresist master plate and writing in the DVD-R format, it is not well known in the related technology that the wobble signal for wobbling the track output from the exposure signal generating apparatus (formatter) which generates the exposure signal for exposing the photoresist master plate is precisely synchronized with the land pre-pit signal.
In regard to the formatter, it can be understood that the wobble signal is generated by the wobble signal generating apparatus, the land pre-pit signal is generated by the land pre-pit signal generating apparatus, a certain phase point during the wobble period of the wobble signal is extracted, a trigger signal is created in order to output the land pre-pit signal in a certain phase relationship with the wobble signal based upon the phase extracting signal, and the trigger signal thus created is output to the land pre-pit signal generating apparatus.
However, in such a formatter as mentioned above, a variation width occurs at the extracted phase point. This variation width is also superposed on the trigger signal. As a result, the precise land pre-pit signal cannot be output.